Run your retirement plan 1,000 times.
A Monte Carlo simulator runs your plan against 1,000 different market histories instead of one optimistic guess, so you see the odds your money actually lasts. No signup, nothing collected, it runs entirely in your browser.
Retirement Reality Check
This is a Monte Carlo retirement simulator. Most retirement calculators hand you one confident number, but real life is a range. It runs your plan 1,000 times against different market histories and shows you every outcome, plus the math behind it.
Your numbers
The result
Run the exact same plan 1,000 times through 1,000 different market histories and the money holds out in 25 of every 100. Markets are the variable. Your inputs stay fixed. An estimate from a simplified model, not a prediction. See the assumptions and limitations below.
Add $100 a month and your odds move from 25% to 29%. That same $100 a month, invested for your 35 working years at the Balanced assumption, grows to about $97,796 in today's dollars. That is the real cost of skipping it.
The cloud of outcomes
Every line your plan could trace. The gold line is the middle outcome. The darker band holds the middle half of all lifetimes. The lighter band holds 8 in 10.
Watch one lifetime play out
A percentage is abstract. Here is one single run, year by year, with the market return it drew each year. This is the engine with the lid off.
How this calculator works
No black box. Here is the formula, every assumption, and every limitation. If you disagree with an assumption, change your inputs and watch the result move.
This is not a prediction, and it is not personalized advice. It is not a recommendation to pick any particular fund, account, or allocation. The result depends entirely on assumptions we chose and listed above, and real markets will not behave exactly like the model. Use it to see the range of what could happen and to understand which inputs move the needle. The decision is yours.
- This is an educational tool. It is not financial, investment, tax, or retirement advice.
- The results are estimates built on assumptions, not predictions. Real market returns will differ from the model, often by a lot.
- The return assumptions are simplified and chosen to teach the idea, not to forecast any real portfolio.
- No number this tool shows is a recommendation to save, spend, invest, or retire in any particular way.
- For decisions about your own money, talk to a licensed professional who knows your full situation.
Common questions
What is a Monte Carlo simulation?
A Monte Carlo simulation runs the same plan many times, drawing a different set of random market returns on each run. Instead of one guess about the future, you get a range of outcomes and can see how often the plan holds up. This tool runs your retirement plan 1,000 times that way.
Is this Monte Carlo retirement calculator free?
Yes. The Retirement Reality Check is free to use, with no signup and no account. It runs entirely in your browser and collects nothing.
Each simulated life draws one random market return per year from a bell curve set by your Balanced mix (average +4.5% after inflation, swing 11%).
Year's return = average + swing * normal random draw
Walk that life year by year. While working, the balance grows by the return and you add $7,200. After age 65, the balance grows by the return and you take out $50,000.
Working: balance = balance * (1 + return) + contribution Retired: balance = (balance - spending) * (1 + return)
Repeat 1,000 times, then count how many lives still had money at age 95. That share is your result: 25% here, which is 246 of 1,000 lifetimes.
Success rate = lifetimes that lasted / 1,000 = 25%
Return assumptions are working placeholders pending CFP/CPA review. The output is a teaching model, not a forecast.
ClearMoneySchool provides educational information only. We are not investment advisors, tax professionals, or attorneys. Nothing on this site is personalized advice. For decisions about your specific situation, consult a licensed professional.
How the simulation works.
This calculator does not reduce to a single closed-form formula; it is a stochastic simulation, so this section explains how the simulation works rather than presenting a step-by-step equation. The three asset-mix mean and standard-deviation return assumptions (conservative 2.5% / 6%, balanced 4.5% / 11%, aggressive 6.5% / 16%) are working placeholders pending CFP/CPA review. They are intentionally on the conservative end of long-run history to avoid overpromising outcomes.
Assumptions
- Returns are normally distributed and independent year to year. Real markets exhibit fat tails and serial dependence (momentum, mean reversion).
- Three asset-mix return assumptions are working placeholders. CFP/CPA review pending; flagged in the PR.
- Contributions stop and withdrawals begin at the retirement age you enter; both happen in a single annual lump.
- Withdrawals are a constant annual nominal dollar amount (no inflation adjustment, no variable spending policy).
- No taxes on contributions, growth, or withdrawals. Real outcomes depend on account type (Roth vs Traditional) and tax bracket in retirement.
- No Social Security, pension, or other income streams during retirement.
Limitations
- Normal-distribution returns underestimate the frequency of extreme years; real history has fatter tails.
- Sequence-of-returns risk (bad years EARLY in retirement) is captured by the simulation but not flagged separately; the success-rate number alone hides this.
- 1,000 trials is enough for stable summary statistics but the tails (the worst 50 outcomes) can still vary between two runs of the same inputs unless the random seed is fixed.
- No inflation modeling. A 4% nominal balanced return is meaningfully smaller in real (after-inflation) terms.
- No glide-path modeling (gradually shifting from aggressive to conservative through working years and retirement).
- It is not a forecast of any specific market's actual return.
- It is not a retirement plan. A real plan handles Social Security claiming, tax-deferred vs Roth withdrawal sequencing, healthcare costs, and changes in spending over decades.
- It is not personalized advice. The asset-mix return assumptions are placeholders pending CFP/CPA review; the success-rate number can shift meaningfully when those numbers are revised.
- It is not a substitute for an actual retirement professional for households where the answer matters.
Common questions.
What is a Monte Carlo simulation?
A Monte Carlo simulation runs the same plan many times, drawing a different set of random market returns on each run. Instead of one guess about the future, you get a range of outcomes and can see how often the plan holds up. This tool runs your retirement plan 1,000 times that way.
Is this Monte Carlo retirement calculator free?
Yes. The Retirement Reality Check is free to use, with no signup and no account. It runs entirely in your browser and collects nothing.
The three fundamentals under the hood.
The Retirement Reality Check rests on three fundamentals. Each one has its own plain-English lesson.
Compound growth. Why the same yearly return turns small contributions into large balances over decades, and why starting earlier matters more than starting larger.
Emergency fund. Sequence-of-returns risk is hardest to absorb early in retirement. A buffer of cash that does not depend on the market is the simplest defense.
401(k) basics. The most common vehicle for the "Adding each year" input in this tool. How contributions, employer match, and vesting actually work.
Educational simulation only. The asset-mix return assumptions are working placeholders pending CFP/CPA review, and the success-rate number can shift meaningfully when those numbers are revised. This tool models no taxes, no inflation, and no Social Security or pension income. ClearMoneySchool does not provide personalized financial or retirement advice.